Dentin is the substance between enamel or cementum and the pulp chamber. It is secreted by the odontoblasts of the dental pulp. The formation of dentin is known as dentinogenesis. The porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water by weight.
Medical Definition of metaplasia. 1  1: transformation of one tissue into another metaplasia of cartilage into bone. 2  2: abnormal replacement of cells of one type by cells of another.
Metaplasia is not synonymous with dysplasia and is not directly considered carcinogenic. It is also contrasted with heteroplasia, which is the abnormal growth of cytologic and histologic elements without a stimulus.ormal physiological metaplasia-such as that of the endocervix is highly desirable. The medical significance of metaplasia is that in some sites where pathological irritation is present cells may progress from metaplasia, to develop dysplasia, and then malignant neoplasia (cancer).